1. Field of the Invention
The present invention pertains to motorcycles with a flexible power transmission mechanism, such as a chain or drive belt, and having cam operated structure for changing the tension in such mechanism, and more particularly, this invention relates to an apparatus and method for use in adjusting the cam operated mechanism to accurately set the tension in the drive belt of the motorcycle having such mechanism.
2. Description of the Prior Art
Wheeled vehicles such as motorcycles generally have a drive sprocket or pulley attached to the drive shaft of the motor. The drive sprocket or pulley is then coupled to a flexible power transmission mechanism. In the case of the drive sprocket, the flexible power transmission mechanism is a chain. Alternatively, in the case of the drive pulley, the flexible power transmission mechanism is a belt.
The chain or belt is coupled to a sprocket or pulley affixed to a driven wheel. The driven wheel is mounted to an axle that is secured to the frame of the motorcycle. Generally the frame of the motorcycle has a forked swing arm and the axle is secured to the swing arm. The swing arm allows bounce, or vertical movement, of the driven wheel. This vertical movement is dampened by a shock absorbing system connecting the swing arm and a rigid portion of the frame.
As is known in the art, the chain or belt must have correct tension to efficiently transfer power from the motor to the driven wheel. Accordingly, chain or belt-tensioning devices have been proposed. Such devices are used to adjust for the natural stretch of the chain. When power is provided or eliminated to the drive sprocket, die chain may be taut on the top or bottom. Particularly in motorcycle chain drives, vibration occurs in normal operation, resulting in a loss of power transfer.
Some motorcycle manufacturers, such as those manufactured by Yamaha Motor Corporation, USA, Kawasaki Motors Corp., USA, American Suzuki Motor Corporation, Ducati Motor Holding S. p. A., integrate a chain tensioner or puller with the driven wheel of their motorcycles. The chain tensioner is coupled to the forks of the swing arm and is placed in a recessed axle slot of the forks. The chain tensioner is attached to the axle of the driven wheel.
In another known tension adjusting device, two tension adjusters are provided and joined to each side of the axle member that engages a guide recess of the forks of the frame member. A threaded adjustment stud in each tension adjuster contacts a respective fork to move the axle member in an adjustment slot to adjust the tension of the chain. In operation, separately adjusting the two studs independently of one another may result in the opposite sides of the shaft being pulled differently and the tension in the chain being other than expected.
In many of the current models of motorcycle, such as those manufactured by Harley-Davidson, a chain or belt tensioner includes two cams, and two guide plates, the cams being joined to the opposite ends of the driven shaft, and the guide plates being joined to the opposite sides of the motorcycle frame and forward of the driven axle. The belt tension is adjusted by rotating a first hex head fixedly joined to one cam, wherein both cams are simultaneously rotated and their respective cam surfaces progressively engaged with their respective guide plates. This rotation pushes the driven axle within an axle bore that is opened within the recessed guide of the forks. Thereafter, a second hex head on the other end of the drive shaft is threadably advanced towards the frame and to drive the cams into gripping engagement with the forks.
However, in operation, the mechanic must hold the first hex head stationary, while rotating the second hex head. As a result, torque placed on the driven shaft by the second hex head being secured thereto may cause the first head to rotate by a small amount. This will result in a back off (i.e., move the shaft back), thus changing the desired tension that was set.
It is to be appreciated that there is a need for a tensioning arrangement that ensures that the tension that is set in the belt during tensioning remains the tension in the belt following tensioning.